/**
 * Copyright 2010 The Apache Software Foundation
 *
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.hadoop.hbase.util;

import java.io.Serializable;

/**
 * A generic class for pairs.
 * @param <T1>
 * @param <T2>
 */
public class Pair<T1, T2> implements Serializable {
	private static final long serialVersionUID = -3986244606585552569L;
	protected T1 first = null;
	protected T2 second = null;

	/**
	 * Default constructor.
	 */
	public Pair() {
	}

	/**
	 * Constructor
	 * @param a operand
	 * @param b operand
	 */
	public Pair(T1 a, T2 b) {
		this.first = a;
		this.second = b;
	}

	/**
	 * Constructs a new pair, inferring the type via the passed arguments
	 * @param <T1> type for first
	 * @param <T2> type for second
	 * @param a first element
	 * @param b second element
	 * @return a new pair containing the passed arguments
	 */
	public static <T1, T2> Pair<T1, T2> newPair(T1 a, T2 b) {
		return new Pair<T1, T2>(a, b);
	}

	/**
	 * Replace the first element of the pair.
	 * @param a operand
	 */
	public void setFirst(T1 a) {
		this.first = a;
	}

	/**
	 * Replace the second element of the pair.
	 * @param b operand
	 */
	public void setSecond(T2 b) {
		this.second = b;
	}

	/**
	 * Return the first element stored in the pair.
	 * @return T1
	 */
	public T1 getFirst() {
		return first;
	}

	/**
	 * Return the second element stored in the pair.
	 * @return T2
	 */
	public T2 getSecond() {
		return second;
	}

	private static boolean equals(Object x, Object y) {
		return (x == null && y == null) || (x != null && x.equals(y));
	}

	@SuppressWarnings("rawtypes")
	@Override
	public boolean equals(Object other) {
		return other instanceof Pair && equals(first, ((Pair) other).first) && equals(second, ((Pair) other).second);
	}

	@Override
	public int hashCode() {
		if (first == null)
			return (second == null) ? 0 : second.hashCode() + 1;
		else if (second == null)
			return first.hashCode() + 2;
		else
			return first.hashCode() * 17 + second.hashCode();
	}

	@Override
	public String toString() {
		return "{" + getFirst() + "," + getSecond() + "}";
	}
}